Rheological Tests Research Articles

Anti-temperature anti-salinity anti-shear C18MAAC / NaAA Amphiphilic Copolymer: Preparation, characterization and properties

For improving the temperature resistance, salt resistance and shear resistance of conventional copolymers, the new hydrophobic monomer C18MAAC was prepared by substitution, then C18MAAC/NaAA amphiphilic dicopolymer was prepared by micellar polymerization. The synthetic parameters were optimized using the single-variable method: reaction temperature 50°C, mass fraction of initiators to the total monomers 0.7 wt%, mass fraction of hydrophobic monomer C18MAAC to NaAA and C18MAAC 2 wt%, and the mass fraction of two monomers 25 wt%. The structure of the C18MAAC and the C18MAAC/NaAA copolymer were characterized, and the morphology of the copolymer was observed. Effect of mass fraction of the copolymer and the salt, temperature, shear rate on viscosity of the aqueous solution were investigated. With the increase of copolymer's mass fraction, the viscosity of the aqueous solution increased slowly first, and the viscosity increases rapidly after reaching 0.4 wt% of copolymer concentration. Therefore, 0.5 wt% concentration of copolymer aqueous solution was selected in the experiment, and the rotor was selected for the rheological performance test. The results showed that the temperature resistance, salt resistance and shear resistance of the copolymer reached 90 °C, 1 wt% salt and 150 s-1 respectively. The C18MAAC/NaAA copolymer/surfactant composite system is very stable in 1wt% salt at 90 °C, and has good synergistic effect to improve the viscosity of the solution, which making it is a promising candidate as an oil-displacing agent.

Study of the liquid resistance effect of water-in-oil emulsions in porous media

During heavy oil recovery in the Bohai Oilfield, substantial emulsification of oil and water occurred, primarily forming water-in-oil (W/O) emulsions. This phenomenon could alter fluid dynamics within the subsurface porous media, potentially impacting well production performance. To elucidate the properties of water-in-oil emulsions and their associated liquid resistance effects, this study conducted a series of rheological tests, microscopic examinations, and injection experiments. The results show that the droplet size and distribution of water-in-oil emulsions were primarily influenced by shear rate and water content, which in turn modified emulsion viscosity. The stability of water-in-oil emulsions was reduced when they flowed through porous media. The increase in emulsion viscosity and the liquid resistance effect collectively enhanced the seepage resistance of water-in-oil emulsions flowing through porous media. Notably, when the emulsion droplet size exceeded the pore throat size, over 90% of the total seepage resistance was attributable to the liquid resistance effect. Conversely, when the majority of the emulsion droplets were smaller than the pore throat, the viscosity accounted for more than 60% of the seepage resistance. Water-in-oil emulsions flowed through cores with permeabilities ranging from 50 to 100 mD, exhibiting threshold pressure gradients between 35 and 43 MPa/m. At a core permeability of 300 mD, the threshold pressure gradient was significantly reduced to 1 MPa/m. The presence of a water-in-oil emulsion in the reservoir could result in a production pressure differential falling below the threshold pressure, thereby reducing reservoir productivity.

Viscous Elastic Asphalt Characteristics of Cariphalte Modification with Addition of Gilsonite Viewed from Phase Angle Value

Performance Grade (PG) Bitumen is bitumen that is graded based on its performance at different temperatures. In the Superpave grading system, asphalt binders are classified according to their performance in extreme hot and cold temperatures and are referred to as performance grade (PG) asphalt. The main objective of assessing and selecting asphalt binder using the PG system is to ensure that the binder has properties suitable for the environmental conditions in the field. Cariphalte is a premium grade polymer modified bitumen used in road and airport construction and other similar applications. Cariphalte is a Styrene Butadine Styrene (SBS) modified bitumen. The SBS in Cariphalte ensures the formation of a 3-dimensional network in the bitumen thereby reducing the temperature susceptibility and increasing the stiffness modulus at high temperatures. Cariphalte is also resistant to oxidation, reducing deformation and slowing secondary solidification. To get an idea of the improvement in rheological properties due to the addition of gilsonite, tests were carried out on a mixture of cariphalte and gilsonite asphalt with 6 variations of gilsonite content. The tests carried out include basic rheological properties testing and mechanistic rheological properties testing. From this research, the test results showed that at the same temperature, asphalt with the addition of 0% gilsonite had the smallest phase angle (δ) compared to asphalt using the addition of gilsonite. This explains that the addition of gilsonite can increase the phase angle (δ) value of PG-76 asphalt, which makes the asphalt material have thicker characteristics.

Mechanochemical preparation and performance evaluations of bitumen-used waste polypropylene modifiers

The value-added recycling of waste polypropylene (PP) as asphalt modifiers has been a popular research topic in recent years, but high blending temperatures and asphalt smoke emissions are difficult issues that have not been solved. Therefore, this study innovatively used phthalic anhydride (PA) and catalysts (NHPI or BPO) to mechanochemically turn waste PP into different reaction products as bitumen-use PP modifiers (PPM(N) & PPM(B)). To well understand the physicochemical characteristics of PPMs, thermogravimetric analysis, torque rheology, and scanning electron microscopy were adopted and analyzed. Furthermore, the penetration, softening point, viscosity, storage stability, and dynamic shear rheology (DSR) tests were also carried out to study the performance differences of their PP modified asphalt (PPMA(N) & PPMA(B)). The main results showed that the PPM(N) continues being degraded with PA, but BPO-degraded PP conversely gets chemical connections with PA. With the effects of NHPI and BPO, all PPMs can improve the deformation resistance of virgin bitumen, even at higher temperatures, but as the PA content increases, this performance will gradually deteriorate for PPMA(N) and shows a slight improvement for PPMA(B). The appropriate use of PA can decrease the mixing temperature of PPM(N) with virgin bitumen and improve the storage stability of PPMA binders, and will not significantly sacrifice the resistances of its PPMA(N) to deformation, while with the addition of PA, the mixing temperatures of PPM(B) and virgin bitumen will not be decreased as expected and the resistances of PPMA(B) to deformation remain unchanged. Overall, the proposed mechanochemical method can work out to well address the high-quality recycling and reuse issue of waste PP for its large-scale application in asphalt pavement.

Effects of Eucommia ulmoides leaf powder on the gelatinization, rheology, and gel properties of sweet potato starch

This study aimed to explore the feasibility of employing Eucommia ulmoides leaf powder (ELP), which is a novel medicinal and food homologous material, to improve the physicochemical properties of sweet potato starch (SPS) gel. The effects of ELP on the gelatinization, rheology, and gel properties of SPS were investigated. The Brabander viscosity test results showed that ELP could reduce the peak viscosity, trough viscosity, final viscosity, and setback value of SPS. The rheological tests showed that the SPS-ELP gels had shear-thinning behavior, and that the ELP could decrease the apparent viscosity, shear stress, G′, G″ of SPS-ELP gels and make the gels exhibit stronger liquid-like behavior. The X-ray diffraction pattern indicated that the ELP could decrease the relative crystallinity and retard retrogradation of SPS-ELP gels, which was cofirmed by microscopic structure analysis. The ELP had a significant effect on the color difference of the gels, resulting in a yellow-green color. The addition of ELP also reduced the hardness of SPS-ELP gels, and increased the median particle size D50, volume mean diameter D [4,3], and area mean diameter D [3,2] of gel particle size distribution. These findings suggest that ELP has a good potential in improving starch gel properties.

Evaluation of rheological behavior and self-healing performance of calcium sulfate whisker-reinforced polyurethane modified asphalt

This study prepared calcium sulfate whisker (CSW) reinforced polyurethane (PU) composites and innovatively used them in asphalt modification to improve the strength and toughness of asphalt. The rheological and self-healing properties of asphalt modified by CSW-reinforced PU (CRP) were evaluated through rheological and self-healing tests. The results indicated that CRP enhanced the modified asphalt's high- and low-temperature properties and fatigue resistance. Compared with matrix asphalt, the high-temperature performance of PC22 is improved by 76.8 %; Tg,DMTA is reduced by 3.61°C; the fatigue life is increased by 2.9–4.5 times. However, excessive CSW tends to absorb more lightweight constituents, leading to a decrease in both low-temperature performance and fatigue resistance. Self-healing tests show that CSW-reinforced PU can improve the self-healing performance of asphalt by 64.7 % compared to matrix asphalt. It is believed that the bridging effect of CSW and the cross-linked network of PU play a key role together. Of the dosages tested here, the optimal dosage of CSW was 10 % by weight of PU, and the optimal dosage of CRP was 20 % by weight of asphalt. This study confirms the feasibility of CRP for asphalt modification and provides a method to achieve high-performance modified asphalt that can be used on roads in cold areas and airport pavements. In addition, CSW's partial replacement of PU can significantly reduce the cost of polyurethane modified asphalt pavement.

Time–Temperature‐Transformation (TTT) Cure Diagram of an Epoxy–Amine System

AbstractA time–temperature‐transformation diagram is created for the curing reaction of a diglycidylether bisphenol A (DGEBA)‐based epoxy resin. It results from a kinetic analysis performed by means of dynamical differential scanning calorimetry (DSC) measurements; a gelation curve determined with isothermal and dynamical rheological tests; and a vitrification curve obtained from temperature‐modulated dynamic DSC measurements. The resulting diagram is validated by comparison of isothermal measurements with the corresponding calculated curves.

Influence of vinyl acetate content on the performance of alkyl fumarate copolymers as crude oil flow improvers

Paraffin deposition during waxy crude oil transportation may obstruct the effective flow and pose serious flow assurance issues. Therefore, copolymers are used as flow improvers (FIs) and pour point depressants (PPDs) during chemical treatment programs. The performance of the copolymers is affected by their structure, particularly by the proportion of polar and non-polar segments. Fumarate copolymers are promising PPDs and FIs for waxy crude oils. However, research on the impact of different molar ratios of polar to non-polar units is limited. In this study, dialkyl fumarate–vinyl acetate copolymers with similar molar weights but different comonomer ratios were synthesized. Rheological tests of Akshabulak crude oil doped with the prepared additives and pour point measurements revealed that the efficiency of the synthesized FIs depended on the vinyl acetate content. The most effective performance was achieved from the copolymer with 58–59% (mol) of vinyl acetate. Thus, the efficiency of crude-oil FIs based on alkyl fumarate copolymers can be improved by changing the monomer ratio.

The influence of rice bran oil and nano-calcium oxide into bitumen as sustainable modifiers

Bio-oils are increasingly used to enhance petroleum bitumen’s intermediate and low-temperature characteristics regarding their economic and environmental benefits. Research has shown a beneficial impact of nanomaterials on altering bitumen’s high-temperature characteristics. The present study uses a mixture of rice bran oil and nano-calcium oxide to improve the performance of bitumen in all three temperature conditions. Rice bran oil was added to pure bitumen at doses of 3, 5, and 7 % relative to the weight of bitumen. The rheological tests (dynamic shear rheometer, multiple stress creep recovery, linear amplitude sweep, and bending beam rheometer) demonstrated that using rice bran oil in bitumen enhanced its performance at intermediate and low-temperatures but declined its performance at high-temperatures. Therefore, to improve the performance at high-temperatures, the bituminous sample containing 5 % rice bran oil was combined with 1, 3, and 5 % nano-calcium oxide, followed by repeating the rheological tests on them. The samples modified with nano-calcium oxide showed increased friction and shear stress, viscosity, and rutting parameters. Besides, the samples exhibited reduced sensitivity to aging compared to the bio-oil samples. However, the non-recoverable creep compliance and percentage of recovery showed improvements. The fatigue life of bio-oil samples decreased after adding nano-calcium oxide. However, the fatigue life remained higher than the base bitumen sample when adding 1 % nano-calcium oxide. Fourier-transform infrared spectroscopy analysis showed that a new chemical reaction occurred due to adding nano-calcium oxide to bitumen containing rice bran oil. Besides, the scanning electron microscope image revealed that the nano-calcium oxide particles are uniformly and homogeneously distributed within the bitumen sample containing 5 % rice bran oil. Consequently, the mix containing 5 % rice bran oil and 3 % nano-calcium oxide increases the resistance against high-temperature failures and improves the low-temperature performance compared to the base bitumen sample.

Effect of sepiolite on the rheological properties of shear thickening fluid and improvement mechanism analysis

To improve the performance of shear thickening fluids (STFs), we propose the addition of fibrous sepiolite. Through macroscopic rheological tests and microscopic characterization, the effects of different sepiolite mass fractions (0 wt%, 1 wt%, 2 wt% and 3 wt%) on the shear thickening of a SiO2-STF system (with a PEG200 dispersion medium) at different ambient temperatures (20 °C, 30 °C, 40 °C and 50 °C) were investigated. Rheological experiments revealed a significant improvement in the shear thickening of SiO2-STF with the addition of sepiolite (Sep/SiO2-STF), with 7.11- and 1.94-fold increases in absolute and relative shear thickening, respectively. As the sepiolite mass fraction increased from 0 wt% to 3 wt%, the temperature sensitivity coefficient decreased from 13.493 to 4.839, indicating that the Sep/SiO2-STF system still exhibited favourable shear thickening at 50 °C. Dynamic oscillatory shear testing revealed that with an increase in sepiolite mass fraction from 0 wt% to 3 wt%, the maximum energy storage modulus, maximum energy dissipation modulus and shear stress increased by 5196.25 %, 1676.16 % and 377.54 %, respectively. Microscopic characterization revealed that sepiolite induced the formation of more clusters in the STF system primarily through the physical adsorption of silica particles and Si–OH on its surface, leading to a significant increase in the shear thickening effect.

Rheological and structural properties of nanofluids based on hydrolyzed polyacrylamide and aminated carbon nanotubes for enhanced oil recovery

Polymer flooding, a prominent enhanced oil recovery (EOR) technique, involves injecting polymers such as partially hydrolyzed polyacrylamide (HPAM) to increase water viscosity for more effective oil displacement. Overall, HPAM exhibits good shear stability, thermal tolerance, and cost-effectiveness; however, it has limitations such as temperature constraints and salinity susceptibility. Integrating nanomaterials into HPAM-based EOR is a promising and innovative strategy, with aminated carbon nanotubes standing out as a strong candidate due to their remarkable tensile strength, excellent thermal conductivity, exceptional chemical and physical stability, and good dispersibility and versatility. This study employed ethylenediamine-functionalized oxidized multiwalled carbon nanotubes (MWCNTO-EDA) as an additive in HPAM solutions for EOR applications. Extensive analyses, including FTIR, Raman, TGA, zeta potential, elemental analysis, and cryo-TEM, confirmed the chemical composition and morphology of HPAM and the nanomaterials. Cryo-TEM images under various ionic conditions revealed that the presence of salts caused polymer chain contraction into spherical structures, explaining the reduced viscosity in high-salinity nanofluids. Rheological tests at 70 °C demonstrated that MWCNTO-EDA significantly increased the nanofluid viscosity over reference HPAM fluids. Notably, nanofluids containing 0.5 % MWCNTO-EDA exhibited an average 55 % viscosity increase at an ionic strength of 0.6, which is vital for applications in EOR where heightened viscosity is crucial. Aging tests, performed over 180 days at 70 °C, displayed substantial viscosity improvements in nanofluids containing 1.0 % MWCNTO-EDA, achieving up to a 150 % increase over reference samples. MWCNTO-EDA emerges as a valuable additive for creating innovative nanofluids, addressing critical limitations and preserving HPAM conformation, making it suitable for EOR in challenging environmental conditions.

Incorporation of cross-linked/acetylated tapioca starches on the gelling properties, rheological behaviour, and microstructure of low-salt myofibrillar protein gels: Perspective on phase transition.

This study investigated the gelling properties, rheological behaviour, and microstructure of heat-induced, low-salt myofibrillar protein (MP) gels containing different levels (2%, 4%, 6%, and 8%, w/w) of cross-linked (CTS) or acetylated (ATS) tapioca starch. The results indicated that either CTS or ATS significantly enhanced the gel strength and water-holding capacity of low-salt MP gels (P < 0.05), an outcome verified by the rheological behaviour test results under different modes. Furthermore, iodine-staining images indicated that the MP-dominated continuous phase gradually transited to a starch-dominated phase with increasing CTS or ATS levels, and 4% was the critical point for this phase transition. In addition, hydrophobic interactions and disulphide bonds constituted the major intermolecular forces of low-salt MP gels, effectively promoting phase transition. In brief, modified tapioca starches possess considerable potential application value in low-salt meat products.

Characterization of hemp seed oil emulsion stabilized by soap nuts (Sapindus mukorossi) extract

In the past years, plant-based surfactants such as plant proteins, hydrocolloids, and extracts have intrigued scientific studies of food formulations for usage in emulsion, nanoemulsion as well as microemulsion systems, mainly due to their functional benefits and low toxicity levels. In this work, a hemp seed oil-containing (HSO) emulsion system was stabilized using soap nuts (SN), also known as Sapindus mukorossi. In order to determine the formulation requirements and the optimal emulsion composition including oil and surfactant content, a Box-Behnken experimental design was applied. The compositions were evaluated in terms of their particle size distribution, stability, visual quality, turbidity, and zeta potential. Moreover, to describe the physicochemical characteristics of the emulsions, rheological tests, Fourier transform infrared spectroscopy (FTIR) analyses, and refractive index parameters were also studied. The average particle size of the emulsions (particle distribution by number) was recorded between 51 and 103 nm, and z-ave parameter reached values between 227 nm and 311 nm. The zeta potential increased when the proportion of HSO increased, and reached its highest value (−23.5 mV) when HSO was 5% v/v. Microscopic investigations confirmed the polydispersity of the prepared emulsions. Furthermore, due to further applications of the emulsions i.e. packing and delivery, wetting properties were evaluated. The wetting angle values reached maximum approx. 30° with an HSO content of 1%. However, the wetting angle values were lower with increasing HSO content. Presented results revealed that Sapindus mukorossi is indeed a good stabilizer for hemp seed oil and water emulsions.

A study of the temperature-dependent stress yielding behavior of a gelatin-based hydrogel ink and its effects on the enhancement of the 3D printing resolution

Though existing studies had continuously improved the hydrogel printing resolution by facilitating ink solidification, it was literally challenging to exceed the size limit of the printing needle even if there was an ideal ink that could solidify instantaneously. One possible solution to this hurdle is to stretch the hydrogel ink with a high printing speed and try maintaining its deformation without strain recovery. In this study, a gelatin/alginate/hydroxyapatite(HA) ink was printed at multiple temperatures, and a much lower yielding strain occurred at −1 °C than 2–5 °C according to our rheological tests. At −1 °C, the hydrogel ink could be highly stretched to produce an ultrahigh resolution at 81 ± 13 μm while maintaining uniform and continuous. Furthermore, our biological tests found a high scaffold resolution greatly promoted cell adhesion, proliferation, osteogenic differentiation and biomineralization. We stepped further from existing studies, by coming up with a new concept of utilizing ink stress-yielding in improving printing resolution, which would broaden our understanding to the processing-structure-property relationship in hydrogel-based 3D printing.

Gas channeling control with CO2-responsive gel system in fractured low-permeability reservoirs: Enhancing oil recovery during CO2 flooding

During the CO2 flooding process in fractured low-permeability oil reservoirs, the injected CO2 is prone to channeling along fractures due to severe reservoir heterogeneity, resulting in poor development effect. The CO2-responsive gel system shows dual advantages in achieving CO2 capture and plugging gas channeling to enhance oil recovery. This paper constructed a system with good CO2 sensitivity based on long-chain alkyl amide propyl dimethyl tertiary amine first. Subsequently, the properties of the system before and after the response were evaluated through rheological test, and its microstructure was characterized by Cryo-TEM. The system exhibited good CO2 responsiveness, transitioning from low-viscosity solution system to high-viscosity CO2-responsive gel system upon contact with CO2, with its viscosity increasing by nearly five orders of magnitude. The CO2-responsive gel demonstrated excellent shear resistance, viscoelasticity and shear self-repairing ability. The change of microstructure further verified the mechanism of molecules self-assembly in the system under the action of CO2. Then, a series of core physical simulation experiments were carried out to comprehensively evaluate the effects of different factors on the injection capacity, plugging characteristics, dynamic filtration damage performance and EOR effect of CO2-responsive gel. The gel maintained injectability while achieving an exceptional deep plugging effect, and the plugging rate reached 98.77%. It showed good characteristics of low filtration and permeability damage in low permeability reservoirs, effectively ensuring the fracture plugging effect. After the fracture was plugged by gel, the sweep range of CO2 to the matrix significantly expanded, and the gas flooding recovery increased by 18.19–21.7%. Finally, the matrix-fracture dual-media chip model was used to conduct microfluidic experiment, the oil displacement characteristics in different displacement stages were visually clarified, and the synergistic plugging and oil displacement mechanism between the CO2-responsive gel and CO2 was summarized. The research results can provide important insights for the green and efficient application of CO2-responsive gel in fractured low-permeability reservoirs.

Phycocyanin-phlorotannin complexes improve the structure and functional properties of yogurt

Adding natural bioactive ingredients to yogurt can improve the nutritional and physiological benefits. In this study, we used ultrasonic-assisted phlorotannin from Ascophyllum nodosum (A. nodosum) modified phycocyanin (PC) to form a complex (UPP) to produce a fortified fermented yogurt. The effects of PC and UPP on the structure, stability, and function of fermented yogurt within 7 days were assessed using physicochemical properties, texture analysis, rheological testing, 16S rDNA sequencing analysis, and lipidomics analysis. Molecular docking indicated that PC might bind to phlorotannin via ARG-77, ARG-84, LEU-120, ALA-81, CYS-82, and ASP-85 sites.When the mass ratio of the complex is 1:1, the ability of UPP1:1 to remove DPPH· scavenging ability in an acid environment increased by about 50 %. UPP1:1 with more acid stability changed the microstructure of the yogurt, enhanced the stability of the yogurt, improved the antioxidant properties, and inhibited the growth of harmful bacteria within 7 days. This work encouraged the extraction and use of phlorotannin from edible brown algae and offered a straightforward method for making yogurt supplemented with PC.

Investigating the influence of stress dependency on the evaluation of high-temperature deformation resistance in SBS-modified asphalt

The rheological responses of Styrene-Butadiene-Styrene (SBS) modified asphalt are stress-dependent, yet the underlying mechanisms and their relationship to the phase structures formed by SBS in the asphalt matrix remain unclear. To address this issue, this study utilized varying dosages of SBS to prepare binders (SBSMA), which were then characterized through fluorescence microscopy, FTIR, and rheological tests including temperature sweeps and Multi-Stress Creep Recovery (MSCR) at four stress levels. Additionally, rutting resistance of the mixtures was evaluated using wheel tracking tests, correlating the results with rheological data. The test results indicate that the formation of a three-dimensional SBS network structure within the asphalt significantly increases the Stress Sensitivity Index (SSI) by 69.5 %, thereby enhancing the binder's stress sensitivity. Based on the theory of entropic elasticity, the stress sensitivity of SBSMA is explained. The cross-linked network structure exhibits superelastic behavior under low stress but may be overstretched and reorganized under high stress, leading to weakened entropic elasticity. Furthermore, the Jnr values obtained at higher stress levels show stronger correlation (r > 0.9) with the Dynamic Stability (DS) from the wheel tracking test results. This finding suggests that entropic elasticity does not significantly improve the rutting resistance performance at the mixture level. Consequently, increasing the stress level in MSCR tests is recommended to more accurately predict the binder’s rutting performance by inhibiting the network's entropic elasticity.

The Diels-Alder Cross-Linked Gelatin/Dextran Nanocomposite Hydrogels with Silver Nanoparticles for Wound Healing Applications: Synthesis, Characterization, and In Vitro Evaluation.

Wound healing involves a sophisticated biological process that relies on ideal conditions to advance through various stages of repair. Modern wound dressings are designed to imitate the natural surroundings around cells and offer properties such as moisture regulation, strength, and antimicrobial defense to boost healing. A recent research project unveiled a new type of gelatin (Gel)/dextran (Dex) hydrogels, linked through Diels-Alder (D-A) reactions, loaded with silver nanoparticles (Ag-NPs) for cutting-edge wound treatment. Gel and Dex were chemically modified to form the hydrogels via the D-A reaction. The hydrogels were enriched with Ag-NPs at varying levels. Thorough analyses of the hydrogels using methods like NMR, FT-IR, and SEM were carried out to assess their structure and nanoparticle integration. Rheological tests displayed that the hydrogels had favorable mechanical attributes, particularly when Ag-NPs were included. The hydrogels demonstrated controlled swelling, responsiveness to pH changes, and were non-toxic. Testing against E. coli showcased the strong antibacterial activity of the nanocomposite hydrogels in a concentration-dependent manner. This investigation showcased the promise of these bioactive nanocomposite hydrogels in promoting speedy wound healing by maintaining a moist environment, offering an antimicrobial shield, and ensuring mechanical support at the wound site.

Advanced optical assessment and modeling of extrusion bioprinting

In the context of tissue engineering, biofabrication techniques are employed to process cells in hydrogel-based matrices, known as bioinks, into complex 3D structures. The aim is the production of functional tissue models or even entire organs. The regenerative production of biological tissues adheres to a multitude of criteria that ultimately determine the maturation of a functional tissue. These criteria are of biological nature, such as the biomimetic spatial positioning of different cell types within a physiologically and mechanically suitable matrix, which enables tissue maturation. Furthermore, the processing, a combination of technical procedures and biological materials, has proven highly challenging since cells are sensitive to stress, for example from shear and tensile forces, which may affect their vitality. On the other hand, high resolutions are pursued to create optimal conditions for subsequent tissue maturation. From an analytical perspective, it is prudent to first investigate the printing behavior of bioinks before undertaking complex biological tests. According to our findings, conventional shear rheological tests are insufficient to fully characterize the printing behavior of a bioink. For this reason, we have developed optical methods that, complementarily to the already developed tests, allow for quantification of printing quality and further viscoelastic modeling of bioinks.

Preparation of a Novel Branched Polyamide 6 (PA6) via Co-Polymerization of ε-Caprolactam and α-Amino-ε-Caprolactam

In this study, a novel branched polyamide 6 has been synthesized via the hydrolytic ring-opening co-polymerization of ε-caprolactam (CPL) and α-Amino-ε-caprolactam (ACL). The NMR characterization proves the existence of a branched chain structure. The rheological test determines that there is a remarkable increase in the melt index (MFR), zero shear rate viscosity, and storage modulus in the low-frequency region. The shear-thinning phenomenon becomes more obvious. The thermal properties tested by differential scanning calorimetry (DSC) show that the melting point and crystallinity of co-polymers decrease with the incorporation of ACL. However, the crystal structure of the samples only exhibits a slight change. When the ACL content in the feed is 1 wt%, the tensile strength and fracture elongation rate of the co-polymers show a significant enhancement.